A vehicle generally includes a transmission on an output side of the drive source to transmit the drive force, that is, the output torque, from the internal combustion or the electric motor, which is the drive source, to the road surface at an optimum condition corresponding to the traveling state of the vehicle. Such transmission may be a continuously variable transmission for controlling the transmission ratio in a non-step wise manner (continuously) or a discontinuous transmission for controlling the transmission ratio in a step wise manner (discontinuously). The continuously variable transmission or a so-called CVT (Continuously Variable Transmission) includes a troidal type continuously variable transmission and a belt type continuously variable transmission. The troidal type continuously variable transmission transmits the torque between each disc through a power roller serving as a transmitting member sandwiched between an input disc, which is a rotation member on the input side, and an output disc, which is a rotation member on the output side, and also tilts the power roller to change the transmission ratio. The belt type continuously variable transmission is configured by a primary pulley, which is a rotation member on the input side that is transmitted with the drive force from the drive source, a secondary pulley, which is a rotation member on the output side for changing the drive force transmitted to the primary pulley and outputting the same, and a belt serving as a transmitting member for transmitting the drive force transmitted to the primary pulley to the secondary pulley, where the transmission ratio is changed by changing the contact radius of the belt and the pulley.
For instance, the troidal type continuously variable transmission sandwiches a rotation means such as a power roller having the outer peripheral surface as a curved surface that corresponds to the troidal surface between the input disc and the output disc including the troidal surface, and transmits the torque using a shearing force of an oil film of the traction oil formed between the input disc, the output disc, and the power roller. Such power roller is supported in a freely rotating manner by a trunnion, which trunnion is rotatable with the rotation shaft as the center and is movable along the rotation shaft by acting a transmission shift control pressing force by the hydraulic pressure of a hydraulic oil serving as a operating medium supplied to a transmission shift control hydraulic chamber (transmission shift control pressure chamber) with respect to a piston arranged in the trunnion.
Therefore, when the power roller supported by the trunnion moves from a neutral position with respect to the input disc and the output disc to a transmission shift position with the trunnion, a tangent force acts between the power roller and the disc thus causing a side slip, the power roller rotates, that is, tilts with the rotation shaft as a center with respect to the input disc and the output disc, and as a result, the transmission ratio, which is the ratio of the number of rotations of the input disc and the output disc, is changed. The transmission ratio, which is the number of rotations of the input disc and the output disc, is determined based on an angle, that is, a tilt angle, the power roller tilts with respect to the input disc and the output disc, and such tilt angle is determined based on an integral value of the stroke amount (off set amount) serving as the movement amount of the power roller from the neutral position towards the transmission shift position.
The troidal type continuously variable transmission adjusts the contacting surface pressure at the contacting portion of the input disc and the output disc, and the power roller to maintain an appropriate traction state by applying a predetermined sandwiching force for sandwiching the power roller between the input disc and the output disc by a sandwiching means. Such sandwiching means acts the sandwiching force of sandwiching the power roller between the input disc and the output disc by applying a pressure of the hydraulic oil serving as the operating medium supplied to the sandwiching force generating hydraulic chamber (contacting surface pressure control pressure chamber).
Such a hydraulic sandwiching means is also arranged in the belt type continuously variable transmission. In other words, the belt type continuously variable transmission acts the pressure of the hydraulic oil serving as the operating medium supplied to the sandwiching force generating hydraulic chamber (contacting surface pressure control pressure chamber) on the pressure acting surface to push a movable sieve towards the fixing sieve, so that the belt sandwiching force of sandwiching the belt between the movable sieve and the fixing sieve is acted, the belt tensile force is adjusted, and the contacting surface pressure is adjusted at the contacting portion of the pulley and the belt.
With respect to the medium pressure control device of the continuously variable transmission of the conventional art, the hydraulic control device of the continuously variable transmission described in patent document 1, for example, supplies the respective discharge oil of first and second oil pumps to line pressure supply destination (e.g., transmission shift control pressure chamber and contacting surface pressure control pressure chamber) by closing a by-pass oil passage in time of rapid transmission shift to suppress lack of oil at the line pressure supply destination, and also communicates a discharge port side of the first oil pump and an intake port side of the second oil pump with a by-pass oil passage at other than in rapid transmission shift so that the second oil pump uses the high pressure discharge oil in the first oil pump to efficiently take in the hydraulic oil and reduce the loss of pump drive, whereby the first and second oil pumps can be efficiently used.
Patent document 1: Japanese Patent Application Laid-open No. 2005-221047